Absorbent felt and artificial leather product made therefrom



Jan; 30, 1934. s. SCHWARTZ ABSORBENT FELT AND ARTIFICIAL LEATHERrnonucw'g MADEEHEREFROM Filed June 9, 1932 George L. Schwafi PatentedJan. 30,15934 UNITED STATES PATENT OFFICE ABSORBENT FELT AND ARTIFICIALLEATHER PRODUCT MADE THEREFROM Application June 9, 1932. Serial No.616,323 18 Claims. (Cl. 92-20).

This invention relates to an absorbent paper, initial material pulp suchas wood pulp composed and more particularly to a felt-like product paroffibers that are long enough (2.0 mm. to 4.0 mm.v ticularly suitable asan impregnating base for the mean fiber length) for making strong paper,

manufacture of artificial leather. The pulp may be made by any of theusual chem- Prior attempts to hydrate paper pulp which ical methods ofmanufacturing paper pulp from has been treated with caustic ofmercerizing the raw cellulose material. The fibers are not strength bybeating the treated pulp with water purified further than that whichtakes place in havebeen generally unsuccessful and have served theordinary sulfate, sulfite, or soda processes no useful purpose. This isevident by the stateof cooking the wood chips in the manufacture of 1ment in the patented art that mercerization the pulp which constitutesthe raw material in tends to lower the strength of the pulp very thepresent process. Rope, flax, hemp and other materially and, on beating,such pulp does not long fibers may be used, providing the fiber length.tend to hydrate or gel, the beating operation has been reduced bycooking or beating, or both, tending to merely macerate or shred thefiber to a fiber length of 2.0 to 4.0 mm. average length. and resultingin a paper of low strength. I have A highly purified pulp is undesirablein the prac- 7 discovered, however, that if the treatment of the tice ofmy invention and I therefore hydrate the pulp with the mercerizingcaustic is conducted ,pulps having a pentosan content above 5% and so asto cause not substantially more than a an alpha cellulose content below94%. superficial mercerization orskin effect, as dis- In producing asuperficially mercerized pulp g9 closed in Patent 1,857,100 issued toFrank H. which is to be subsequently hydrated as described McCormick andmyself, and if the beating of the hereinafter, I proceed in accordancewith the pulp with water is effected in the special manner process setforth in detail in the patent mendescribed hereinafter, a hydrated pulpis obtioned above. Briefly, this consists in dispersing" tained whichmay be made into an absorbent felt the pulp with caustic of mercerizingactivity and having certain remarkable properties particularpromptlydiluting the caustic in contact with the 35 ly adapting it for use an animpregnating base. pulp below mercerizing activity as soon as the v Thisinvention has as an object paper or felt pulp has been dispersed intothe caustic liquor. somewhat denser and of greater strength than Inthepresent process, however, it is not desirable that disclosed in theabove mentioned patent but to use concentrations of sodium hydroxideabove which is still sufiiciently porous to absorb 001- 14% because ofthe long time requiredto hydrate loidal dispersions like the best ragfelts. Anthe pulp by beating itinwater. It is to be under- .other objectis to make from paper making fibers stood, however, that with theexception of this a strong well closed sheet which acquiresmaxidisadvantage the higher caustic concentrations mum impregnatingstrength with relatively small up to 35%, where the wettingproperties ofthe amounts of saturants. Another object is to solution become verypoor, can be used, but in make a felt having a high residual porosityafter any event the best results are obtained when the saturation withsufiicient material to give satistreatment is conducted so as to preventextended factory strength as a base for artificial leather. time actionof the strong caustic on the pulp. In A further object is'to make a feltwhichhas a the practice ofmy invention, I may use sodium 49 satisfactorypaper break after impregnation with hydroxide concentrations above 6.5%,which is colloidal dispersions. A still further object is to justslightly below the concentration required for provide a new andeconomical process of proa solution of mercerizing activity.A-concentrarducing a strong, absorbent felt suitable for use tion of 8%is preferred. The concentrations as a base for artificial leather andlike products. mentioned are those used at room temperatures. ,5 Otherobjects will appear hereinafter. In order to minimize the drastic actionof the These objects, in the preferred embodiment of caustic on the pulpand to prevent the action of my invention, are accomplished by the stepsthe strong caustic on the fibers from extending which consist intreating ordinary paper pulp beyond a superficial or skin effect, thepulp is withstrong caustic solution under conditions dispersed at highconsistencies, i. e., consistencies 50 which avoid drastic actionbetween the caustic above 10% and'preferably about 18%,.the ratio andfiber such as takes placeinprocesses for makof caustic to pulp at an 18%consistency being ing highly purified or high alpha cellulose pulp, 4.56parts by weight of liquor for one part by and then beating the caustictreated pulp with weight of pulp. The ratio of the treating soluwaterina special manner which causes hydration to the dry fibers is veryimportant for the 55 tion of the pulp without substantial shorteningreasons just mentioned and because of the econof the fiber lengththrough the cutting action omy of operation, reduction of weight loss,as which takes place in the conventional processes well as certainmechanical advantages obtained for beating pulp in 'the manufacture ofhigh by dispersing the pu p with the caustic at h h grade or writingpapers. consistencies. The speed with which the sodium 60 In carryingout my invention, I use as the hydroxide 5011117101! is dispersed into hl i8 pulp is washed or which meshes with .very important, slowdispersion results in obtaining fibers treated with differentconcentrations due to dilution, especially when the moist pulp is used.The best conditions are obtained when a sodium hydroxide solution isdispersed into the pulp instantaneously. A longer time of treatment thanis required for good dispersion of the pulp with the caustic isundesirable chiefly beproduction and increased loss of valuablematerial. The freeness of the pulp treated with the caustic alkalisolution in the manner just described, as tested by the special freenesstester mentioned in the patent noted above, will as a rule vary from 60seconds for a 6.5% caustic treatment to 31 seconds for a 14% caustictreatment, these values being also dependent upon the kind of fibersused.

The mechanism or dispersing the pulp with the caustic and for hydratingthe pulp following the caustic nection with the accompanying drawing inwhich Fig. 1 illustrates a form of apparatus that may be used incarrying out the invention;

Fig. 2 is an elevational view partly in section of another mechanism forcarrying out the invention;

Fig. 3 is a diagrammatical view of the conveyor for supplying themechanism of Fig. 4 with pulp;

Fig. 4 is an elevational view of the upper portion of Fig. 2 showingarrangement of the hopper and conveyor;

Fig. -5 is a plan showing the arrangement of the toothed rollers in themechanism of Fig. 4; and

Fig. 6 shows the conveyor on which the treated washed and felted.mechanism for mixing or dispersing the pulp with the caustic solutionand promptly diluting the caustic in contact with the pulp afterdispersion has been effected, is that shown in Figs. 2 to 6. Air-drypulp compressed into the usual commercial a wire screen conveyor 5 wherea shower 15 of sodium hydroxide solution of 8% concentration at roomtemperature falls upon them. The excess caustic solution which runs offthe sheets is The preferred which tear sheets into pieces of aboutone-half inch in diameter. These rolls are driven by the belt 10 atdifferent speeds, such as r. p. m. and 600 r. p. m., respectively, bymeans of the smaller gear on the driven shaft of the roll 8 the largergear on the shaft of the roll 9. The pulp then drops down in a discrefiner where additional caustic is supplied through pipe 10' in suchquantity as will bring the total amount up to a ratio of 4 partssolution to one part of pulp (20% consistency) As previ-- ously noted,the concentration of the solution may be'made sufficiently higher thanthe final discs 11 and 12 from the mass abrasive action treatment isbetter described in con pulp board is fed onto The discs 11 and 12havesmooth interfitting corrugated faces as shown and are driven in oppositedirections by a mechanism not illustrated at a relatively high speed andare set with a clearance of 1 6 inch to of an inch so that each fiber isfreed from the mass in the passage 13 which extends from the entrance atthe center of the disc to the edges where they are thrown off bycentrifugal force. From this disc refiner the pulp drops into a trough14 where the reaction between the caustic and fibers is stopped bydiluting the caustic which also lowers the stock density to a pumpingconsistency. The duration of the treatment, that is the time elapsingbetween the application of the caustic on the conveyor from pipe 15 andthe deposition of the pulp into the diluted solution in the tank 14, isnot more than 15 seconds. The pulp passes through the conduit 16 to thechamber 1'1 whence it passes over a wire screen 18 where it isformedinto a thick sheet and washed free from excess caustic solution.While fresh water may be introduced into the trough 14 to wash out thecaustic to stop the reaction, I' prefer to use the caustic (below 4%)resulting from the countercurrent washing system on the screen 18 1 soas to avoid dilution of the solution to the point where recovery of thecaustic from the solution is no longer profitable. The numeral 19designates a series of suction boxes between which the washing showersof water are directed. The show 20 is water and the weak caustic washedthrough the sheet into the last suction-box is pumped to the precedingshower forming a stronger solution in the suction box below. Theconcentration progressively increases until the solution in the secondsuction box resulting from the shower 21 contains about 4% causticconcentration which is pumped back into the. tank 14. The solution fromthe first suction box, which precedes the shower 21 and which removesthe excess weak caustic resulting from the treatment of the pulp in tank14, is run into a concentrator for recovering the caustic by raising theconcentration of the solution to the value required for conducting theprocess. After passing over the suction boxes the sheet passes underanother wire screen 22 where it is pressed between two or more sets ofsqueeze has been freed from caustic solution, it may be storedindefinitely as wet laps or in dilute pulp form or as dry pulp, and isready for forming into sheets of felt at any time.

The pulp introduced into the hopper 6 of the disc refiner may be in anyone of several forms such as the dry pulp referred to above whichusually contains from 20% to 5% moisture. The

concentration of the to give the desired concentration of sodium hy- 15seconds.

vroom temperature, that .diificult to hydrate by heating droxide incontact with the fibers. When pulp other than pulpboard is used, it is,of course, not necessary to pass the pulp through the shredding machine;

In the treatment of the pulp with the caustic the temperature is a veryimportant factor and is a temperature between 20-40" C., is preferred.For temperatures below 20 'C. the concentrations of treating liquor mustbe reduced to conform to the increased mercerizing effect. However,treatments at low temperature solutions give products that are much morethan products obtained at room temperature or above. Temperatures above40 C. are avoided because of the considerable degradation of cellulosewhich takes place at higher temperatures.

The beater shown in Fig. 1 may be used also to disperse the pulp withthe caustic as well as to hydrate the superficial mercerized pulp bybeating it in water in the manner described hereinafter. The beaterconsists of a receptacle 1 in which the power driven roll 2 may beraised so that the longitudinal bars 3 may clear the bed plate 4. Thecaustic solution and the air-dry pulp in a ratio to give aconsistencyabove 10% is put into the beater with the roll raisedslightly from the bed plate as shown in the drawing so that the bars 3will squeeze the pulp against the bed plate and separate the individualfibers from the pulp mass and secure contact between the fibers and thecaustic solution and cause wetting of the fibers in the shortestpossible time without any abrasive or cutting action.

The method of ing example:

Kraft pulp from northern sprucefreeness 6'7 .0 seconds, containing 60%moisture (Water in pulp) Sodium hydroxide solution, 12.8% 2,500 poundsConsistency 20 Sodium hydroxide solution in contact with the fibers 8%Temperature of treated pulp 26.0 C.

Freeness of washed, treated pulp"; 51.0 seconds 2,500 pounds 1,500pounds The pulp in wet lap form was shredded into small pieces and wasfed by a belt conveyor continuously into the hopper of the disc refineror pulper in which the sodium hydroxide solution was also fedcontinuously at a rate adjusted to give an outgoing pulp consistency of20%. The treated pulp was completely dispersed in the fibers as it camefrom the discs and it fell into a stream of 4.0% sodium hydroxidesolution within seconds from the time it came into contact with thestrong sodium hydroxide solution. This dilution lowered the consistencyto 0.5%. This suspension was promptly conveyed to a suction filter whereit was washed by the counter current washing system until the alkaliconcentration of the liquid in contact with the fibers was 06% and thepulp consistency was 13.7%. -It was then repulped in suflicient waterand sulfurus acid to make the paper, it was passed over a washer wheremost of the salts were removed and where it was thickened to a 5%consistency. It was then pumped into a Hollander type beater (Fig. 1)where it was beaten with the roll in alight brushing position for eighthours until the freeness was 130 It was then passed through'a Jordanwithout cutting. The consistency was then lowpracticing my invention maybe better-understood by reference to the follow- .sirable for thepurposes diluted pulp neutral to litmus ered to .40 and it was passedover a Fourdrinier machine. The suction filter and washer shown in thedrawing may, if desired, be replaced by a segmented cylinder or washer.

In beating the treated and washed pulp with water the beater roll mustbe close enough to the bed plate to cause pressure and squeezing actionon the pulp but without cutting or abrasion of the fibers. In order toget the proper squeezing action it is important not only that the beaterroll be set at a light brushing position to avoid cutting the fibers,but that the water and pulp be present at a consistency somewhat higherthan is ordinarily used in processes involving beating pulp in water.For this reason I prefer to operate with consistencies between thelimits of about 4% to 5%. While it is possible to operate withconsistencies as low as 3% and as high as 6% this practice isundesirable because of the excessive care required to prevent bruisingor cutting at the lower. consistencies and to prevent overheating withconsequent retardation of hydration at the higher consistencies. Thoseskilled in the art .will understand what is meant by a light brushsetting of the beater roll which does not reduce the freenessappreciably by cutting action. The rollowing is a description of thebeating conditions in terms of units of measurement for a 10 poundlaboratory beater: Consistency of pulp in water-5%; temperature rangeduring beating to 12" x 3" with /8" bars and 1 between bars. bars setdiagonal to beater bars; beater bars broad with 1" spacings; roll-l2face and 14 diameter; peripheral speed of roll-1570' per minute;pressure on bed plate which is movable, 27,000 grams (this pressure isobtained by a leverage ratio of 4:1).

The time of beating, which is usually about beating to a 135 sec.freeness, may range from 2 to 12 hours depending upon the kind of pulp,the manner of its manufacture and the degree to which it has beenmercerized. The temperature during with water should not be allowed torise above C.

The artificial crinkling and superficial mercerization of the pulp, aseffected by the caustic treatment previously desc bed, causes anincrease in freeness whereas its hydration by beating with water lowersthe freeness from its initial value of about 31 seconds to '70 secondsto about to 200 seconds. I prefer to hydrate the pulp to an extent whichbrings its freeness to about 135 seconds. While a more or lesscompletely mercerized or highly purified pulp may be successfullyhydrated by conducting the beating in water under the special conditionsdescribed above, the beating time required is greatly increased and theproduct obtained is less deof the invention. The high freeness of thetreated pulp which is subjected to the hydration treatment and thebeating in water at highpulp consistency with the roll'in a lightbrushing position to prevent abrasion or cutting of the fibers arefactors contributeight' hours when .ing to the fast freeness of myhydrated pulp. A purified or mercerized pulp beaten in the usual way forthe manufacture of high grade papers has a freeness seldom less than 300seconds and which may be as high as 1000 seconds.

0.; bed plate the beating of the pulp It will be understood that thehydration referred to in the present invention is reversible by boilingwith water as distinguished from the hydration caused by caustictreatment which is not so reversible. ance with the present inventionresponds to the conventional tests for the mercerization and hydrationof cellulose fibers. The mercerization of the fibers may be identifiedby viewing them through the microscope and noting the change from thenatural ribbon-like form, characteristic of cellulose fibers, to awire-like form substantially circular in cross section. When themetfreeness obtained by 15 minutes boiling being at least 15%. In someinstances, this reversal of hydration through boiling with water willcause a 90% increase in freeness.

Inasmuch as the pulp treating process described above avoids extendedtime action of the caustic solution on the pulp, the process does notresult in any appreciable purification of the cellupentosans and otherThe product oba 240 pound paper, using a ream base of 25"x38" and 500sheets, is between the limits of 58 to 150 pounds.

Unimpregnated sheets Products corresponding to samples 4, 5, t and 7 inthe above table were obtained by treating the with representativesaturated papers, samples 8 and 9, and with ness of 130 seconds. Thesheets were approximately 0.40" thick and weighed 25.8 grams per 10 x10" area.

The felt produced by the process described in the example above wasimpregnated with natural rubber latex containing 16.0% rubber by acontinuous process in felts, where it was dried at a steam pressure of 8pounds to a moisture content of 8%. ished product had an Elmendorf tearof 1,470

Wh! n bent over a 0.5 mandrel.

Sample No. 3 of the following table shows the properties of the feltwhen impregnated with latex to the extent of 20% rubber based on theweight of the final product:

I mpregnated sheets containing 20 rubber as latex Paper break Elmendorfgz 52x25? diameter of Pliability tear cylinder grams 1 97 1. 0" 21. 0@170 2 3 0. 3 12. 0 1m 3 25 0. 5 16. 0 1470 4 36 0. 6 19. 5 1430 5 14 0.5 16. 0 1100 6 42 0. 3 11. 0 1100 7 28 0. 6 17. 5 1720 8 24 0. 3 14. 51400 9 3 I 0. 5 l2. 5 1150 The base materials in the above table,identified by sample numbers corresponding respectively to the samplenumbers of the ummpregnated sheets with 20% rubber from latex.

An artificial leather productclosely resembling real leather wasobtained by applying the following coats to the impregnated productresulting from the process described in the example:

Kerosene NaOH treatment prior to hydration with water Fromm Porosity bsMullen Saturaursting tlon time seconds seconds g?" strength 15%latexpounds seconds kraft pulp which has been hy-.

Parts unusual advantages as a saturating base, it has Pyroxylin 4. 00other applications that are very useful. Its high Orange shellac 4. 00porosity combined with high strength makes it Ethyl alcoholdenatured'25.00 useful as a dry unimpregnated insulation for Ethyl acetate 22. 50wires, dust filters, heat insulators, blotters and Butyl acetate 2. 50the like. 1

The term colloidal impregnating materia This coat was dried at 105 C.for 10 minutes. It was then given two coats of the followingcomposition, with 15 minute drying periods at 105 C. after each coat:

- Parts Pyroxylin 1.00 Castor oil 1.90 Pigment 0.60 Ethylalcohol-denatured 5.00 Ethyl acetate 4. 50

' Butyl acetate 0.50

The coated material was then embossed in a Skiver grain. The finishedproduct resembled a good grade of heavy leather, could be skived readilyin order to make good glued joints, could be stitched without tearing,and in general could be handled like leather of the same pliability andthickness.

The same result, with minor variations, may be obtained by substitutingfor latex other colloidal impregnating materials such as pyroxylin-oilcompositions, asphalt in toluol solution, shellac in alcohol solution,blown linseed oil in benzol solution, and a latex ofchloro-2-butadiene-1, 3 polymer. Rubber dispersions in organic solventsare, however, less satisfactory as impregnating media. The following areexamples of the type of materials suitable generally as impregnatingmedia; artificial aqueous dispersions of rubber as well as the naturallatex; celluloseesters; cellulose ethers;' polymerizable substances,such as urea-formaldehyde and chloro-2-butadiene-l, 3 polymers;bituminous substances such as bitumens, pyrobitumens, pyro-liquors,distillates, tars, and pyrogenous residues'from. the manufacture ofoils, fatty acids, fats, or waxes; natural resins, such as rosin, damar,copal, shellac; synthetic resins such as glyptals, styrene and vinylresins; waxes such as paraffin, Canauba, and ozokerite; greases such aspetrolatum; drying oils such as blown linseed oil, blown China-wood oil,blown fish oils.

The sheet material impregnated with any of the substances mentioned maybe coated with pyroxylin compositions, blown drying oil compositions,rubber compositions, caseine compositions, etc., for 'the production ofvarious leather products. I

. Very fine pigments in limited ratios" can -'be incorporated into theimpregnating media, and these are carried into the center of the feltwithvout straining. The impregnating base described herein can also beimpregnated satisfactorily with the previously mentioned substances whenthey contain other constituents than pigments, such as dyes that areused for colored pyroxylin compositions, latices, and resins. Some ofthe impregnated products are useful without further treatment. Wherecertain surface effects are required the impregnated products are coatedwith 'cellulose ester compositions,.rubber compositions,

drying oil compositions and the like. In cases where the sheets areimpregnated to the maxi-1 mum limit in order to obtain greater strengthand other properties, such as water resistance, a

primercoat is required like that given in the example.

Although the felt of the present invention has absorbent papers whichthat lamination of types of artificial used herein refers in general tonon-crystalline film forming materials which includes not only truecolloids 'such as latex, but also those impregnating materials which,because of their high viscosity or because of other properties, offerthe same difficulties in the tends to strain out the pigments and largecolloidal particles on the sur-. face and prevent uniform impregnationof the interior of the sheet.

Among the advantages possessed by my improved product the followingmaybe mentioned:

High strength with sufficient porosity to permit dispersions withcolloids or viscous liquids without the sheet breaking or destruction ofthe felt structure; a high impregnated porosity which gives goodanchorage for final coats; less cement or other impregnating material isrequired than in the case of the more porous felts such as the productsin the mentioned patent, or cotton linters and roofing felt, to give theequivalent strength; the impregnated product is resistant to heattreatment after saturation which enables resins such as Bakeliteimpregnated in the sheet to be changed to the infusible st ge. Theimpregnated product has a high pliab' ity, especially when impregnationis followed by embossing.

The sheet absorbs cements uniformly-there is as much cement material inthe interior of the sheets as there is on the surface. The sheet can besaturated uniformly in such great thicknesses The high rate of wettingand saturation of the impregnated base with colloid dispersions is ofdecided advantage in the economic production of impregnated felts;saturated products, especially those that are embossed, freer from paperbreak than felts made from untreated pulps. The process of the presentinvention also makes some low cost raw materials available for new usesin higher price fields. As many apparently widely different embodimentsof this invention may be made without departing from the spirit andscope thereof, it is tov be understood that I do not limit myself to thespecific embodiments thereof except as defined in ,thejollowing claims:

I claim:

1. A process which comprises treating mercerimpregnation of ordinary.

thin sheets is not necessary.

are relatively ized but" substantially ,unpurifled paper pulp ofpentosan content of more than 5% with water until the pulp is hydrated.

2. A process which comprises hydrating mercerized but substantiallyunpurified paper pulp by subjecting the pulp admixed with water at aconsistency within the limits of about 3 to 6.5% to a continuous mixinginvolving a squeezing action without any substantial cutting of thefibers, said mercerized paper pulp having a pentosan content more than5% and an alpha cellulose content less than 94%.

3. A process which comprises beating substantially unpurified mercerizedpaper pulp fibers in water without any substantial abrasive or cuttingaction until the freeness of the pulp is reduced to within the range of85 to 200 seconds.

4. A process which comprises dlspersingpaper pulp with a solution ofcaustic alkali having a strength equivalent to that of a sodiumhydroxide solution above 6.5% at room temperature, washing out thesolution before the action of the causbeyond a superficial or skineffect, and hydrating the pulp by beating it in water withoutsubstantial abrasive or cutting action on the fibers.

5. A process which comprises dispersing ordinary chemical paper pulphaving a mean fiber length of 24 mm. with sodium hydroxide within therange of concentration of 6.5% to 14% at a consistency above 10% and ata from about 20 C. to 40 C., washing out the caustie, and beating thepulp with water at a consistency of about 4% to 5% with the beater rollset at a light brushing position until the freeness is reduced withinthe range of 85 to 200 seconds.

6. A process which comprises dispersing ordiroll set at a light brushingposition until the freeness is reduced to about 135 seconds.

7. A process which comprises dispersing ordihaving a mean fiber 8. Theprocess set forth in claim 5 in which the chemical paper pulp is kraftpulp.

9. The product substantially identical with that obtainable by theprocess set forth in claim 5.

10. The product substantially identical with that obtainable by theprocess set forth in claim 6. 4

content of less than 94%, and a mullen strength of 58 to 150 pounds.

14. An artificial leather comprising a felt of hydrated mercerized paperpulp impregnated with colloidal impregnating material.

15. The product set forth in-claim 12 wherein the colloidalimpregenating material is rubber latex.

16. An artificial leather comprising a felt of hydrated mercerized paperpulp impregnated impregnating material selected from the classconsisting of fatty oil, bituminous materials, resins, rubber, celluloseesters. cellulose ethers, waxes and greases.

1'7. The product set forth in claim 14 wherein the pulp is substantiallyunpurified and has a pentosan content of more than 5%.

18. The product set forth in claim 16 wherein the pulp is substantiallyunpurified and has a pentosan content of more than 5%.

GEORGE L. SCHWARTZ.

